Field of the Invention
The present disclosure relates to a surface emission laser, an information acquisition apparatus, and an imaging apparatus.
Description of the Related Art
In recent years, the research and development of tunable lasers with variable oscillation wavelengths s actively performed because such tunable lasers can be expected to be applied to various fields such as the optical communication field and the examination field. The configuration of moving one of a pair of reflectors of a vertical cavity type surface emission laser (vertical cavity surface emission laser: hereinafter, referred to as a “VCSEL”) is developed as a tunable laser. Specifically, by mechanically moving one (movable mirror) of a pair of reflectors using the Micro Electro Mechanical Systems (hereinafter, referred to as “MEMS”) technique, a cavity length is varied, and the oscillation wavelength of the VCSEL is changed. Such a VCSEL will be hereinafter referred to as an “MEMS-VCSEL”.
A High index Contrast subwavelength Grating (hereinafter, referred to as an “HCG”) in which a subwavelength grating is formed in high refraction index material can be used as a movable mirror. In “1060-nm Tunable Monolithic High Index Contrast Subwavelength Grating VCSEL” (Thor Ansbak and 3 others, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 25, NO. 4, p. 365-367, Feb. 15, 2013), an MEMS-VCSEL using an HCG as a movable mirror is disclosed. Furthermore, in “1060-nm Tunable Monolithic High Index Contrast Subwavelength Grating VCSEL” (Thor Ansbak and 3 others, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 25, NO. 4, p. 365-367, Feb. 15, 2013), the following configuration is disclosed. An HCG is formed of a semiconductor having conductivity, and the HCG is pulled toward the side of an active layer by electrostatic attractive force.
If the HCG formed of the conductive semiconductor is pulled toward the active layer side, the HCG may be deformed by the electrostatic attractive force, and the oscillation of a VCSEL may be inhibited. In other words, if electrostatic attractive force is applied to the HCG, the electrostatic attractive force acts on the HCG itself. Thus, in addition to reducing a distance between the HCG and the active layer, the electrostatic attractive force causes the shape of the HCG itself to easily deform to be a shape protruded toward the active layer side. Accordingly, the reflection direction of light from the active layer changes, and substantial reflectance declines. This leads to an increase in lasing threshold, so that oscillation of the VCSEL is inhibited.